Heretofore, polyimide resins, polybenzoxazole resins, and the like which have an excellent heat resistance, mechanical characteristics, and other characteristics have widely been used for surface protective films, interlayer dielectric films, and the like for semiconductor elements of electronic equipment. When polyimides and polybenzoxazoles are used for surface protective films or interlayer dielectric films, one of the methods for forming through-holes and the like is etching using a positive-working photoresist. However, this method is problematic in that the processes of applying and releasing a photoresist are needed, and complicated. In this regard, heat-resistant materials with photosensitivity imparted thereto have been reviewed in order to streamline working processes.
Usually, a coating film of a precursor of a polyimide or a polybenzoxazole is thermally cyclodehydrated to thereby afford a thin film having an excellent heat resistance and mechanical characteristics. In this case, high temperature baking at about 350° C. is usually needed. However, for example, MRAM (magnetoresistive random access memory), which is promising as next generation memory, is susceptible to high temperature. On that account, in order to be used for surface protective films of such elements, polyimide resins or polybenzoxazole resins which can be cured by baking at a low temperature of approximately 250° C. or less and achieve performance favorably comparable to that of conventional materials baked at a high temperature of approximately 350° C. are demanded.
Examples of methods for obtaining polyimide resins or polybenzoxazole resins which are cured by baking at low temperature include addition of a ring-closing promoter, a method in which to introduce into a unit structure an organic group for promoting ring-closing at low temperature, a method in which to use a polyimide or a polybenzoxazole which is preliminary ring-closed after having alkali solubility imparted thereto, and the like.
In another respect, when a heat-resistant resin composition is used for applications for semiconductors and the like, the heat-cured film remains as a permanent film in a device, which means that the properties of the film cured after being heated are very important. To secure reliability in semiconductor packages, the adhesion to a material formed on the surface of a semiconductor chip is important. In particular when a heat-resistant resin composition is used for applications such as an insulating film between wiring layers of a wafer level package, the adhesion to a metal material used for electrodes and wiring is important. There is a problem, however, in that a resin composition containing a resin that can be cured at low temperature has a low adhesion to metals used as these wiring materials. It is generally considered that, because of having a rigid main-chain structure, a heat-resistant resin has an adhesion strength that is not high to a metal material, and particularly in a cured resin film formed out of a resin composition with photosensitivity imparted thereto, the composition includes additives such as a photosensitizer, a sensitizer, an acid generator, and a solubility adjusting agent, which still remain in the cured film after heat-curing, resulting in the cured resin film having a lower adhesion strength than one which does not contain such additives.
Further, along with a demand for a higher degree of integration, smaller size, and higher speed, recent semiconductor packages have led to having a structure in which wiring and insulating films are formed in multiple layers even on such a cured resin film which has been formed, and cured resin films have been required to have chemical resistance to withstand such processes. Polyimides and polybenzoxazoles are originally resins that have a high chemical resistance, but when they have photosensitivity imparted thereto or when they are baked at low temperature, the cured resin film may have an insufficient chemical resistance because additive components remain therein. As a solution to these, the enhancement of chemical resistance due to a film density increased by adding a thermal acid generator or a polymer crosslinking agent has been considered (see Patent Literature 1 and 2). By carrying these out, however, the adhesion to a substrate tends to become even lower, and materials which can achieve both high chemical resistance and adhesion to wiring are demanded.
Specific examples of methods for improving the adhesion to metal materials include: positive-working photosensitive resin compositions composed of an alkali-aqueous-solution-soluble polymer, a photo-acid generator, and a silane compound containing 4 or more specific functional groups bound directly to an Al atom, a Ti atom, or a Si atom (see Patent Literature 3); and heat-resistant resin precursor compositions composed of a heat resistance resin precursor such as a polyimide precursor and of a specific amino compound or a thiol derivative (see Patent Literature 4).